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CVE-2021-43784

Published: 6 December 2021

runc is a CLI tool for spawning and running containers on Linux according to the OCI specification. In runc, netlink is used internally as a serialization system for specifying the relevant container configuration to the `C` portion of the code (responsible for the based namespace setup of containers). In all versions of runc prior to 1.0.3, the encoder did not handle the possibility of an integer overflow in the 16-bit length field for the byte array attribute type, meaning that a large enough malicious byte array attribute could result in the length overflowing and the attribute contents being parsed as netlink messages for container configuration. This vulnerability requires the attacker to have some control over the configuration of the container and would allow the attacker to bypass the namespace restrictions of the container by simply adding their own netlink payload which disables all namespaces. The main users impacted are those who allow untrusted images with untrusted configurations to run on their machines (such as with shared cloud infrastructure). runc version 1.0.3 contains a fix for this bug. As a workaround, one may try disallowing untrusted namespace paths from your container. It should be noted that untrusted namespace paths would allow the attacker to disable namespace protections entirely even in the absence of this bug.

Notes

AuthorNote
alexmurray
The original advisory notes this is likely not exploitable on runc versions < 1.0.3 so I have assigned this a low priority.

Priority

Low

Cvss 3 Severity Score

5.0

Score breakdown

Status

Package Release Status
runc
Launchpad, Ubuntu, Debian
jammy Not vulnerable
(1.0.3-0)
bionic Needed

focal Not vulnerable
(1.0.3-0)
hirsute Ignored
(end of life)
impish Ignored
(end of life)
upstream
Released (1.0.3)
trusty Ignored
(end of standard support)
kinetic Not vulnerable
(1.0.3-0)
lunar Not vulnerable
(1.0.3-0)
xenial
Released (1.0.0~rc7+git20190403.029124da-0ubuntu1~16.04.4+esm4)
Available with Ubuntu Pro
mantic Not vulnerable
(1.0.3-0)
Patches:
upstream: https://github.com/opencontainers/runc/commit/d72d057ba794164c3cce9451a00b72a78b25e1ae

Severity score breakdown

Parameter Value
Base score 5.0
Attack vector Network
Attack complexity High
Privileges required Low
User interaction None
Scope Unchanged
Confidentiality Low
Integrity impact Low
Availability impact Low
Vector CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:L